Revista Brasileira de Ensino de Fı́sica, v. 33, n. 2, 2601 (2011)
www.sbfisica.org.br
História da Fı́sica e Ciências Afins
Liquefaction of gases and discovery of superconductivity: two very
closely scientific achievements in low temperature physics
(Liquefação de gases e a descoberta da supercondutividade: dois feitos cientı́ficos na fı́sica de baixas temperaturas
intimamente relacionados)
Simón Reif-Acherman1
School of Chemical Engineering, Universidad del Valle, Sede Meléndez, Cali, Colombia
Recebido em 15/11/2010; Aceito em 15/3/2011; Publicado em 3/6/2011
Liquefaction of helium and the discovery of superconductivity are two of the most striking developments in
low temperature physics. The fact that both were carried out in the laboratories of Kamerlingh Onnes at Leiden
is not mere coincidence; the first one was indispensable for the researches that led to the second one. On the same
way, liquefaction of helium was the consequence of several decades of efforts addressed to the process for liquefy
the so-called then ‘permanent gases’. A whole study of this remarked subject must then include developments
that extended, in his decisive step, more than a half of a century and that connect researches of many scientists
throughout several European countries.
Keywords: liquefaction, superconductivity, electrical conductivity, electrical resistance, helium, electron theory.
A liquefação do hélio e a descoberta da supercondutividade são dois das mais surpreendentes desenvolvimentos da fı́sica de baixas temperaturas. O fato que ambas ocorreram no laboratório de Kammerlingh Onnes em
Leiden, na Holanda, não é mera coincidência: o primeiro foi indispensável para que os pesquisadores pudessem
chegar à segunda. Do mesmo modo, a liquefação do hélio culminou após décadas de esforços em liquefazer os
chamados “gases permanentes”. Um estudo mais completo deste assunto requer a discussão de estudos que se
estenderam por mais de 50 anos, ligando pesquisadores de diferentes paı́ses europeus.
Palavras-chave: liquefação, supercondutividade, condutividade elétrica, resistência elétrica, hélio, teoria de
elétrons.
1. Introduction
The study of the remarkable properties exhibited by
the matter in the vicinity of the absolute zero became
one of the main research subjects carried out in the
second half of the XIX century and the first decades of
XX century in low temperature physics. The discovery of new phenomena derived from these researches
decisively contributed to the dramatic changes that affected and characterized a wide group of scientific and
technological disciplines on the following times. Superconductivity, whose first centenary is commemorated
this year, is, very probably, the most striking of them.
The observation of the abrupt drop in the electrical
resistance of mercury wire to an immeasurably small
value as it is cooled below at a certain temperature was
the culminating development of a entire research program carried out by the by the Dutch physicist Heike
Kamerlingh Onnes at his cryogenic laboratory at Leiden, which had begun about three decades earlier.
1 E-mail:
sireache@univalle.edu.co.
Copyright by the Sociedade Brasileira de Fı́sica. Printed in Brazil.
One of the most important sources for those changes
was helium, the chemical element first detected by the
French astronomer Pierre-Jules-César Janssen (18241907) in 1868 in India through a bright yellow line he
observed in spectroscopic study of the chromosphere
during a total eclipse of the sun [1], and latter recognized as different to those then known by the astronomer Joseph Norman Lockyer (1836-1920), in collaboration with the English chemist Edward Frankland
(1825-1899) [2]. Once some the first sources of helium
were identified in earth, and along the full century, its
unique physical and chemical properties, such as low
boiling point, density and solubility, and inertness, respectively, progressively allowed a lot of remarked developments in so diverse fields, as for example astronomy, cryogenics, medicine, electronics, power generation, communications, energy storing and transportation systems, among others.
The liquefaction of helium by first time on July 10,
1908 not only put end to a race that involved scientists
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from different countries with the same objective, but
opened up a whole new field of research. The first part
of this article is mainly concentrated in the researches
carried out at the University of Leiden, and focuses on
the different details that characterized the initial steps
of the whole program of liquefaction of those so-called
‘permanent’ gases and how each chapter of the full story
contributed in different measure to the successful obtaining of liquid helium at Leiden. It is subsequently
shown the way how the apparatuses, cryogenic facilities and strategies developed along this program became the indispensable infrastructure that three years
later would lead to the discovery of the phenomena of
superconductivity.
2.
The basic facts and the state-of-art
of liquefaction of gases in the beginnings of XX century
As whatever successful technology, the closed relationship between academic research and industrial innovation, besides appropriate communication and commercial good sense, were the ingredients for the early developments on low temperature physics. The underlying basic motivations can then be looked from different
viewpoints.
Several elements contributed to the increasing interest on the very particular behavior of substances at
low temperatures at the end of the XIX century and its
possible applications. Liquefaction of gases was then
the most important experimental tool and source of
information to get it. Initial trials with ammonia by
the Dutch chemist Martinus van Marum (1750-1837)
in 1769 [3], and others with chlorine by the English
chemist and physicist Michael Faraday (1791-1867) in
1823 [4], showed the possibility to liquefy a gas only
by compression, and varying both pressure and temperature, respectively. The works carried out on the
concept of critical temperature, first on its existence
by the French physicist Charles Cagniard de la Tour
(1777-1859) in 1822-1823, and four and half decades
later by the Irish physician and chemist Thomas Andrews (1813-1885) on the clarification of its nature and
hence the relationship between the gaseous and liquid
states of matter, supplied a theoretical basis to previous
successful trials of liquefaction [4].
From a practical viewpoint, the each time more observed necessity about the use of cold in different areas
of preservation of foods, as for example fermentation of
some brewing industries and intercontinental shipment
of meat, together with the growing concern about the
utilization of natural ice from frozen polluted sources of
water, had stimulated the development of new equipments for making artificial ice, such as vapor compression and absorption refrigerators [5].On the other hand,
the increasing unpopularity of known refrigerants as
Reif-Acherman
ammonia and sulfur dioxide at that time, because of
their hazardous or toxic nature, had began to arouse
scientific interest to turn the attention to utilize new
compounds for this just purpose, which coincide with
the recent discovery of those we now know as noble
gases. The possibility to evaluate quantitatively different properties of substances for confirming or rejecting
emerging or established scientific theories, or for implementing new and more accurate measuring instruments
for each one of them, became an additional motivation
for studying these new ranges of temperature. Electrical resistance, as it is shown below, was one of these
properties [6].
The definitive step had happened in 1877 with the
practically simultaneous but independent liquefaction
of the first “permanent” gas, oxygen, by the French
mining engineer Louis Paul Cailletet (1832-1913) [7]
and the Swiss physicist Raoul Pierre Pictet (18461929) [8], using two different methods. Whereas Cailletet’s involved high compression, then mild cooling,
and finally a sudden decrease in pressure, Pictet’s consisted of a series of stages during each of which a different gas was liquefied by exploiting the corresponding thermodynamic properties of the preceding stage.
Very quickly other European scientists, as the Polish
Zygmunt Wróblewski (1845-1888) and Karol Olszewski
(1846-1915) at the Chemistry Department of the Jagiellonian University in Cracow, took interest in the same
subject, tried some improvements in the equipment and
the operating techniques, and extended the whole field
of research. Although different gases were studied, the
interest was mainly focused in two of them: hydrogen
and helium.
3.
The liquefaction of hydrogen as
starting point and a false claim of
priority
The liquefaction of oxygen put end point to the concept
of “permanent gases”, and after that nobody doubted
about the possibility to turn other gases into the liquid state. Hydrogen was the following step. The efforts
were then focused on substantial improvements over the
original Pictet’s method, then known as the cascade
process. The researches followed then two simultaneous and dependent on each other lines: the quest of
each time more lower temperatures, and investigation
of properties of substances in these new ranges.
The main protagonists of the hydrogen’s chapter,
that by first time -although mistakenly- involved helium, were the Dutch professor of experimental physics
and meteorology at the University of Leiden Heike
Kamerlingh Onnes (1853-1926) - Fig. 1 -, and the Scottish professor of chemistry at the Royal Institution in
London -later Sir- James Dewar (1842-1923). They had
the same ultimate objective, but great differences in
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
their investigative attitudes and motivations.
2601-3
different properties of matter was his main objective.
His words reveal a more scientific interest on the subject. “The territory of low temperatures,” he said, “has
always tempted the experimenters. . . The arctic regions
in physics incite the experimenter, as the extreme north
and south [poles] incite the discoverer” [13]. He based
the whole program for the liquefaction of gases on the
experimental verification of the theories of his compatriot and friend Johannes Diderik van der Waals (18371923), which served him as motivation to seek lower
and lower temperatures to investigate the properties of
matter. The publication of van der Waals’s thesis on
the continuity of the states [14], five years before the liquefaction of oxygen and almost completely ignored by
Dewar, not only had showed the first theoretical breakdown of the Boyle’s law, but supplied a general frame
to the procedure for the development of the cryogenic
researches and the design of the corresponding equipment.
Figura 1 - Heike Kamerlingh Onnes (1853-1926). Credit: Courtesy of the Kamerlingh Onnes Laboratory, Leiden Institute of
Physics, University of Leiden.
Dewar, who got involved in low temperature research around the middle of 1880’s, didn’t see the theory as complement to the experiment into the physical
research, as it is shown by the fact that no one theoretical paper can be found through the extensive group
of publications on liquefaction or other subjects along
his full career. His was an absolutely practical interest,
directed to the identification of new techniques for lowering the temperature and purifying gases [9]. In 1892
he was able to use his invention of the double walled
silver glass vacuum vessel that actually bears his name
to store cryogenic liquids for some long periods of time.
On May 10, 1898 he collected by first time approximately 20 cm3 of liquid hydrogen in five minutes by
using the Joule-Thompson effect at adapting an interesting process developed by the German engineer Carl
Paul Gottfried von Linde (1842-1934) [10]. Based on
wrong analysis of previous information and on experimental restrictions [11], Dewar concluded that hydrogen and helium have almost identical boiling points,
and publicly communicated to the Royal Society, and
to his main “rival” colleague, the simultaneous liquefaction of both compounds (Fig. 2).
It was shown very quickly that what Dewar thought
was liquid helium were really traces of impurity, and
that the objective for liquefy helium must to wait for a
next opportunity and other circumstances. As far as his
publications reveal, and probably due to his remarked
proud and polemic personality, he never admitted explicitly his mistake in public.
Kamerlingh Onnes, by his side, had a very different
motivation and philosophy [12]. The study of the general character of the influence of low temperatures on
Figura 2 - Telegram from Dewar to Kamerlingh Onnes (1898).
Credit: Courtesy of the Museum Boerhaave.
4.
The work at the cryogenic laboratory
in Leyden
At a fully reconstructed laboratory, superbly equipped
with the sophisticated apparatus he required, and
adapting what he considered the best ideas of other
researchers, Kamerlingh Onnes embarked on two main
purposes [15]. The first one was an extensive and systematic program to measure the volumetric properties
of a great variety of pure substances over the widest
possible range of conditions, which, in light of van der
Waals’s law of corresponding states, might enable him
to predict their properties at low temperatures [16].
The development of his virial equation of state, with
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twenty-five parameters dependent in a different way on
temperature, helped in this purpose [17]. The equation,
which expresses the product of the pressure of a gas and
its molar volume as a finite polynomial series expansion
in powers of the inverse molar volume, was a tool for
understanding better the real behavior of gases. The
second purpose was the production of large quantities
of liquefied gases that he required for the experiments,
work that was preceded by a very careful process of
purification of each substance under study; for the moment there was no matter that it seemed that he was
behind the achievements of his ‘rivals’.
The laboratory had been methodically built stepby-step, and the whole process corresponded with an
improved version of the original cascade method with
two cycles used by Pictet to liquefy oxygen, which progressively included a larger number of cycles [18]. In
each cycle a different gas circulated. It consisted of
three basic elements, a condenser or liquefier, a vessel in which the liquid was evaporated at low pressure,
and one or more vacuum pumps, which evacuated the
gas from the evaporation vessel and compressed into
the condenser. According to the arrangement, each cycle operated at a lower temperature than the preceding
one. So, the evaporation vessel on one cycle simultaneously functioned as the condenser of the next one. The
circulation of the fluid through the system was simple: the liquefaction by compression of the gas circulating at low temperature was followed by evaporation
at low pressure, being the vapor pumped back to the
compressor, after which the cycle started again. With
the evaporation, the reached temperature in the lowpressure chamber was less than that corresponding to
the critical point of the fluid used in the following cycle
(Fig. 3).
Kamerlingh Onnes inspired the choice of the substances of the two first cycles on previous experiences
by Cailletet. By 1894 he had constructed a large scale
plant with four cycles of methyl chloride, ethylene, oxygen and air, which allowed him to reach temperatures
of -193 ◦ C and product fourteen liters of liquid air per
hour [19]. After solve between 1896 and 1898 serious
obstacles related with the prohibition by the Municipality of Leiden to perform in the laboratory experiments
with compressed gases, Kamerlingh Onnes faced with
a new objective: liquefy hydrogen. He understood that
could not use his cascade method with hydrogen, because its critical temperature is far below the lowest
temperature that he could reach at the time, and there
was not suitable gas available for a cycle between that
with air and the one planned with hydrogen. By applying van der Waals’s law of corresponding states, he
was able to predict the properties of hydrogen at those
lower ranges of temperature, and, as Dewar did, incorporated the Linde process to his general scheme. In
1906 the laboratory included a hydrogen cycle as fifth
cycle, reached a temperature of about -253 ◦ C, and an
Reif-Acherman
initial production of four liters per hour, which very
quickly extended to thirteen.
Figura 3 - Diagram for the cascade for liquid gases from 1906.
Credit: Courtesy of the Nobel Foundation.
5.
The successful liquefaction of helium
Although it was true that air and hydrogen were liquefied at Leiden seventeen and eight years, respectively,
after these events happened by first time, the Laboratory was at the beginning of XX century in a far more
advantageous position than those similar in other European countries. The difference was based on three
main aspects: a more careful scientific planning, an installation with equipment infrastructure capable of producing easily large quantities of liquid air and liquid hydrogen, and a remarkable diplomatic skill put at service
of solving all those difficulties different to those strictly
technical. This last distinctive fact allowed Kamerlingh
Onnes to solve problems that ranged from getting funds
or different supplies to unexpected events that in some
way could retard the activities in the Laboratory.
By 1895 sources of helium were found on earth.
Working at the Washington Laboratory of the Geological Survey, the American chemist William Francis
Hillebrand (1853-1925) observed the evolution of a gas
at treating powder of the mineral uraninite with sulphuric acid [20]. According to routine analytical procedures, he thought the compound was nitrogen. Sir
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
William Ramsay (1852-1916) repeated later the experiments, and sent samples to Lockyer and Sir William
Crookes (1832-1919), who spectroscopically found absolute coincidence with the yellow line given by the helium of the sun [21]. The compound was independently
and almost simultaneously discovered in other uranium
mineral, cleveite, by the Swedish chemist Per Theodor
Cleve (1840-1905) and his student Nils Abraham Langlet (1868-1936) [22]. Although in 1905 the American
chemists Hamilton Perkins Cady (1874-1943) and his
student David McFarland (1878-1955) discovered what
would be the first industrial source in the extraction
from natural gas [23], the available amounts of helium
were definitively limited. Besides technical facts, this
was one of the main obstacles for the liquefaction.
In 1896 Olszewski did the first attempt to liquefy helium. The substance was obtained from Ramsay [24].
The only marked difference between the two series of experiments he carried out was the refrigerant he used; in
the first one he utilized liquid oxygen, and in the second
one liquid air. By the evaporation of the liquid refrigerant under a pressure of 10 mm Hg, the lowest temperature he reached was around -220 ◦ C. Even at this
temperature, and with a pressure of 140 atmospheres,
the following sudden expansion to even atmospheric
pressure didn’t give him any evidence of liquefaction.
He tried again nine years later with the same method,
but this time with helium extracted from a radioactive
mineral called thorianite, recently discovered in Ceylan, which was then considered the richest source of
this gas (about 9-10 cubic centimeters of helium per
gram), and using liquid hydrogen as refrigerant [25]. In
spite of work at more extreme conditions, -259 ◦ C and
180 atmospheres, he was again unable to get successful
results. Understanding that the lack of the financial
means necessary to build the appropriated apparatus
he would like to get was an obstacle that he could not
solve, and still with doubts about the real possibility
to liquefy this gas, Olszewski definitively desisted from
his effort.
Halfway between the two Olszewski’s trials other
persons made also clear their interest on the subject
of liquefaction. In a Bakerian lecture delivered in 1901
Dewar did reference to some unsuccessful experiments
he carried out performing a similar procedure to that
by his Polish colleague [26]. The source for helium was
now the gas evolved from the water of the King’s well
at Bath, a little English city built in the mouth of an
extinct volcano, located just outside of Bristol in the
country’s southwest region. A look to some pages of his
laboratory notebooks complements this information [9].
Along approximately three years he worked on the subject, isolating enough helium for his experiments and
producing the amount he calculated would require of
liquid hydrogen as refrigerant in the equipment. Technical difficulties, bad health, and the little confidence
he had in his assistants forced him to eventually give
2601-5
up trying.
Independently, the British chemist Morris William
Travers (1872-1961) did other unsuccessful attempt.
From middle of 1890’s Travers had closely worked with
Ramsay in the search of missing elements which the periodic law indicated should exist. In this way, it were
discovered other rare gases as neon, krypton and xenon,
and some of the properties of the five new gases, including argon and helium, were determined. In 1901 he
required liquid hydrogen for the cooling step in the liquefaction process to separate a helium-argon mixture.
As Dewar never published a description of his apparatus, Travers found himself in the necessity to build
his own with the with the limited resources of a small
compressor, a small air liquefier and £50 to cover all
additional expenditure, and the only help of the laboratory mechanic who carried out the connecting work.
The liquefier operated successfully with only a trial [27].
With this record, and together with his compatriot, the
also chemist George Senter (1874-1942), and the French
physicist Adrien Jaquerod (1877-1957), he proposed try
to find the probable values of the critical and boiling
points of helium, and attempt liquefy the gas [28]. Previously Travers himself had unsuccessfully tried to fractionate helium by absorption by the platinum splashed
on the walls of a vacuum tube that the German mathematician and physicist Julius Plückner (1801-1868) had
designed for the determination of trace elements present
in solid state samples through using a glow discharge
source [29].
The new research was an appendix to a whole work
focused on the relationship between the thermodynamic
scale of temperature and the various scales of temperature as it was experimentally determined by means of
gas thermometers on one side, and the determination
of the vapor pressures of liquid hydrogen at very low
temperatures on the other. Hydrogen and helium were
then considered the most important thermometric substances. The mineral cleveite was the initial source for
obtaining pure helium. The equipment consisted of a
compression tube of an apparatus similar to that employed by Cailletet (see Fig. 4). The wider portion, A,
was capable of standing a pressure of 80 atmospheres,
or more, being the compression apparatus connected
to its lower end. It was required a pressure of 60 atmospheres to compress the whole of the helium in the
capillary tube B cooled with liquid air, which passed
through a rubber stopped E into a small silvered vacuum vessel C filled with liquid hydrogen. There were
two gauges gathered with the tube to make the measurements in different ranges of the variable. It was
provided a plug of natural wool in the upper part of
the tube D to shield the mouth from external radiation. The internal pressure at the vessel was measured
by a mercury manometer connected to the tube F . A
vacuum vessel H, filled with liquid air, enclosed the
tube D. A reduction in the pressure of liquid hydrogen
2601-6
by means of the pumps connected through the tube G,
that caused decreasing in temperatures to values that
were estimated below to -260 ◦ C didn’t lead, nevertheless, to some evidence of liquid helium. Although it’s
true that the experimenters observed the near impossibility to do liquefaction with equipments as used, they
didn’t dare to do definitive conclusions about the feasibility in other circumstances. What they definitively
brought up was the necessity to do extensive studies on
the Joule-Thomson effect of helium over a wide range
of temperatures to learn its real response, cooling or
heating, at be undergone to free expansion at high or
at low temperatures.
Figura 4 - Hydrogen liquefier used by Travers. Credit: Ref. [27].
The profound interest Travers had in the promotion of the university scheme in the University College
at Bristol, where he worked, and the later offer to take
up the post as first Director of the then proposed Indian Institute of Science at Bangalore, finally accepted
in 1909, forced him to interrupt his work on liquefaction [30]. After his retirement of the Institute in July
1914 and his arriving back to England he embarked on
different activities, and never returned to researches on
low-temperature physics.
In spite of the helium’s discovery on earth happened
in an unplanned way thirteen years after Kamerlingh
Onnes undertaken his work at low temperatures, the
research leading to its liquefaction had a very special
meaning for the Dutch scientist. The study, or ‘attack’
on helium, as he said, was “the boldest attack that can
be dreamt of in low temperatures” [31]. Helium allowed him to get several times nearer to absolute zero
than was possible with hydrogen. He faced up to the
subject of liquefaction of helium in a very similar way
as he did with the previous gases. Remaining faithful to his belief about take the van der Waals’s law
of corresponding states as a guide of his full research
program, he defined as first step the determination of
Reif-Acherman
helium’s isotherms, particularly for those temperatures
that could be obtained by means of liquid hydrogen.
As in the past time, he was sure it was the more suitable way to calculate its critical properties, and through
them determine the conditions for the liquefaction [32].
The first worry Kamerlingh Onnes had was how to
have access to enough quantities of helium. Knowing
that Bath springs were a good option (the helium content there was about one-thousandth part of the gas
evolved from the water of the thermal springs), he contacted the authorities there inquiring about the possibilities to get it there, but they referred him to Dewar.
In the letter that Kamerlingh Onnes sent to the British
scientist let him know the state of advance of his investigations and the urgent necessity he had to undertake
immediately the determination of the isotherms. Some
typical features of Dewar’s personality had to presume
that the answer would not be favorable, as indeed it
was. Although it is true that the relationship between
both scientists was cordial, and that they exchanged information and discussed various difficulties they faced
in their experimental research, Dewar was a selfish person that didn’t like generally to collaborate with other
scientists and regarded them as his rivals. At his answer
Dewar said “It is a mistake to suppose the Bath supply
is so great. I have not been able so far to accumulate
sufficient for my liquefaction experiments. If I could
make some progress with my own work the time might
come when I could give a helping hand which would
give me great pleasure”. He added that “I have in my
own way been engaged on this subject for years and after many misfortunes, and with not little expenditure I
have been unable to accomplish my specific object. We
both want the same material in quantity from the same
place at the same time and the supply is not sufficient
to meet our great demands” (cursive is mine) [33].
Kamerlingh Onnes didn’t remain waiting if Dewar
would be able to honor his promise, and look for other
alternatives. Helium could to be isolated too from monazite sand, a primary ore of the same radioactive origin as thorianite, but composed of several phosphates
of many of the rare earth metals along with cerium,
lanthanum and thorium. It approximately contained
1-2 cubic centimeters of helium per gram. The original process comprised heating of the mineral to 1000
◦
C, being the escaped helium subsequently purified by
treatment with hot metallic calcium, which absorbs nitrogen and other gases [34]. In 1905 the mineral was
temporally mined at North Carolina for uses as source
of thorium for incandescent mantles, and Kamerlingh
Onnes was able to obtain large quantities of it under favorable conditions thanks to the efforts of his younger
brother Onno (1861-1935) who was then Director of
the Office of Commercial Intelligence in Amsterdam
[35]. Few years later, and taking advantage of the mediation of the American chemist and pioneer of radiochemistry Bertram Borden Boltwood (1870-1927) who
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
had previously visited the Leiden Laboratory, Kamerlingh Onnes would receive two free of charge invoices of
helium gas from the Austrian scientist and industrial
Carl Auer von Welsbach (1858-1929), founder of Welsbach Light Co., which produced the mentioned mantles by processing large quantities of thorianite (whose
treatment was significantly less expensive), in return of
important amounts of the waste of the monazite sand
treatment, which still contained thorium) [36].
The next step was the careful and perseverant
preparation of enough helium of high purity with the
assistance of Gerrit J. Flim (1875-1970), the chief of
the technical department of the Cryogenic Laboratory,
the glassblower Oskar Kesselring, and four chemists.
The basic procedure used at Leiden consisted of heating and purifying monazite at low temperatures in a
series of stages that included adsorption on charcoal.
The isotherms were ready two years later. According
to them, he was able to estimate the helium’s critical
temperature around 5 K, or maybe slightly higher. This
value calmed him down a little. Along their attempts
of liquefaction Olszweski and Dewar had estimated the
critical temperature closed to 2 K, and he had predicted
a similar value. If it had been a true, liquefy helium was
an almost impossible experimental objective.
By 1908, Kamerlingh Onnes had obtained 360 liters
of helium of high purity, and had been able to produce in his laboratory more than 1500 liter of liquid
air, more than enough for the operation of his cascade
system. It was necessary include a fifth cycle. He was
then focused on the design and latter construction of
the helium liquefier and the elimination of the contamination from glycerin, the lubricant he used in his
vacuum pumps. The liquefier was a closed imitation
of the model of that of hydrogen. All the system had
to be reduced to a smaller scale, approximately half
size, because the limited availability of helium and the
capacity of the pumps. Larger reductions had led to
construction problems. One of the more operating difficulties was the simultaneous work of hydrogen and
helium cycles. Although it is true that this one must to
be the most appropriate option, the installed infrastructure was not enough for it. Based on the unquestionable
fact that was more difficult obtain liquid hydrogen than
liquid helium in the required quantities, it was decided
on one hand allow the latter to circulate, forcing the
quantities not liquefied pass several times through the
cycle, and on the other have previously prepared and
stored large amounts of hydrogen. This decision was
later confirmed a very good one, because helium must
pass twenty times through the cycle before liquefaction
was observed.
An undated telegram for Dewar, found among the
Kamerlingh Onnes’s papers, and that very probably
corresponds to few months before the liquefaction, reveals what at the first time was a fleeting excitement,
but some time later turned into frustration. The ob-
2601-7
served solidification of some impurities of helium initially suggested that could correspond to the pure element. The reasons Kamerlingh Onnes found for the
misinterpretation in the traces between 0.45 and 0.37
volume percent contained in the gas used in the experiments, suggested him the necessity to improve the
purification method.
On July 10, 1908, Kamerlingh Onnes was able to
produce more than 60 cubic centimeters of liquid helium in an experiment “that bordered on the impossible” [37], lasting more than 14 hours. A detailed and
chronological account of the events was related by the
scientist [35, 37]. A diagrammatic scheme of the full
helium cycle is shown in the Fig. 5. The work began
at 5:45 a.m. when were prepared and ready to use 20
liters of liquid hydrogen, which were stored in silvered
vacuum glasses. After be sure that there was no contamination in each piece of the full arrangement, it was
proceeded at 1:30 p.m. to the filling with liquid air and
liquid hydrogen to protect the glasses in the hydrogen
and helium cycles, respectively. At 4:20 p.m. helium
was circulating through the liquefier (see Fig. 6). Fifteen minutes later the pressure of the helium began to
be slowly increased from 80 to 100 atmospheres, and
one hour after that the first trial with a sudden expansion to 40 atmospheres occurred. The temperature
was then around 6 K. Several new trials were done, and
even using the last available bottle of liquid hydrogen
still nothing was observed.
Figura 5 - Helium’s cycle in the cascade process. Credit: Ref.
[35].
That Kamerlingh Onnes had actually produced liquid helium might have passed unnoticed owing to his
very low surface tension and consequently the absence
of a clear boundary between its gaseous and liquid
phases. Thus, all of Kamerlingh Onnes’s careful planning and extensive building of his cryogenic apparatus
- the most sophisticated in the world at this time might not have borne fruit, at least not for some time,
had someone outside of his team of researchers not noticed that the bottom of his vessel was improperly il-
2601-8
luminated and hence did not permit observation of the
gas-liquid boundary layer [38]. However, as he wrote,
“After the surface had once been seen, it was no more
lost sight of. It stood out sharply defined like the edge
of a knife against the glass wall” [35]. The presence
of that helium liquid, “that looked almost unreal”, was
absolutely confirmed when it had already filled up the
vessel. It happened at 7:30 p.m. and the corresponding
measurement of temperature, 4.25 K, was the minimum
one up till then experimentally reached.
A commemorative stone of grey marble related with
this event that was placed in the building where then
was the Laboratory still stays there (Fig. 7). It was put
on by its staff some years later to pay homage to Kamerlingh Onnes. In it are carved the following words: “On
this spot, on the 10th of July, 1908, Helium was liquefied for the first time by Dr. Heike Kamerlingh Onnes.
The entire staff of the laboratory has presented to him
this memorial on the occasion of the 40 anniversary of
his professorate. November 11th , 1922”.
Figura 6 - Helium liquefier. Credit: Ref. [35].
Reif-Acherman
Figura 7 - Commemorative stone for helium’s liquefaction.
Credit: Courtesy of the Museum Boerhaave. Credit: Courtesy
of RCC Koude & Luchtebehandeling.
6.
Superconductivity is on the way
It is interesting to note that if it is true that the first
part of the whole program of researches in low temperatures at Leiden was specially focused on liquefaction of
gases and related areas, the subject of electricity, and
specifically the behavior of electrical properties in the
same zone, not only arose the interest of Kamerlingh
Onnes from the beginnings of his work, but also became one of the parts of what he called “the unity of
natural phenomena” [39]. It is clearly revealed in his
lecture on the importance of quantitative research on
the occasion of his appointment as professor of experimental physics at the University of Leiden in 1882, in
which Kamerlingh Onnes devoted an appreciable portion to different electrical subjects [40].
Contrary to what is a widely diffused belief, the researches on the behavior of the resistance of metals as
a function of temperature in Leiden, which later would
led to the discovery of superconductivity, did not begin in 1908 after the successful liquefaction of helium.
The program of a general investigation at Leiden on the
relation between the electrical resistance and temperature on the ranges under study there, including different metals, was officially communicated in 1902 [41]. Its
initial objectives, as the following papers mainly bearing on electrical measurements showed, were focused on
thermometric applications [42, 43].
The state of the art on the subject in those times
showed significant advances, which had been specially
complemented in the second half of the XIX century
thanks to the facilities provided in the range of temperatures opened by the researches on liquefaction of
gases. The first significant achievements went back to
the Italian physicist Gianbattista Beccaria (1716-1781)
[44], and later the English scientist Henry Cavendish
(1731-1810), who, through the earliest experiments carried out on the electrical conductivity of various substances [45], were able to show the superior conductivity of metals. The researches were followed by the
also British physicist Humphry Davy (1778-1829), who,
working in the Royal Institution in London, showed in
1821 by first time that the electrical conductivity of
wires of different metals, such as platinum and silver,
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
decreases with increasing temperature [46].
The experimental researches strengthened with the
extensive series of measurements made in 1835 by the
Russian physicist H.F. Emil Lenz (1804-1865) in St.
Petersburg. Working at temperatures far above 0 ◦ C,
he proposed that the electrical conductivity of metals
varies quadratically with their temperature [47]. In
1858 the Norwegian physicist Adam Arndtsen (18291919) at the University of Christiania (later Oslo) concluded that it was the electrical resistance and not the
electrical conductivity of most of pure metals under
study in similar ranges of temperatures which varies
linearly with temperature [48]. His paper immediately
caught the attention of Rudolf Clausius (1822-1888) at
the Polytechnicum (later the Eidgenössische Technische Hochschule) in Zurich, who concluded that “the
resistance of a simple metal in the solid state is closely
proportional to the absolute temperature” [49]. Subsequent measurements by August Matthiessen (18311870) at the University of London, however, called
Clausius’s conclusion into question [50].
A new chapter in the story was opened in 1885 with
the report by Cailletet and Edmond M.L. Bouty (18461922) of resistance measurements of several metals (aluminum, copper, iron, magnesium, mercury, platinum,
silver and stain) down to the boiling temperature of
ethylene (-100◦ C) [51]. Previously bismuth, a metal
of commercial interest in the last quarter of the nineteenth century, had been the subject of the researches of
the Italian Augusto Righi (1850-1920)[52], the French
Anatole Leduc (1856-1937) [53]and the Belgian Edmond van Aubel (1864-1941) [54]. Working separately
they published a detailed report of the behavior of its
electrical resistance and those of its alloys for moderately low temperatures. The Polish scientist Zygmunt
Wróblewski (1845-1888), who together with his compatriot Karol Olszewski (1846-1915) had improved Cailletet’s method in Cracow and had been able to liquefy
oxygen, nitrogen, and carbon monoxide [55], extended
even more down the temperatures to reach that of solid
nitrogen (-200◦ C) [56]. Cailletet and Bouty found a
linear dependence of resistance on temperature, while
Wróblewski found a much faster variation. That same
year, the British physicist Hugh Longbourne Callendar (1863-1930), working under J.J. Thomson in the
Cavendish Laboratory in Cambridge, began a systematic series of precision measurements on platinum, that
led him in 1899, now at the University of London, to
propose a parabolic relationship between resistance and
temperature and to become the first one to suggest the
possibility that the resistance of “most of the common
metals” tends to vanish at a temperature higher than
absolute zero [57]. Meanwhile, between 1892 and 1893,
James Dewar at the Royal Institution in London and
John Ambrose Fleming (1849-1945) at University College, London, had carried out an extensive joint series of
resistance measurements, first on eight pure metals and
2601-9
seven alloys [58], and later on fourteen metals [59], down
to the temperature of boiling liquid oxygen (-200 ◦ C).
Kamerlingh Onnes got involved in experimental
work on the subject by first time in February 1906,
once hydrogen had been liquefied in his laboratory and
its availability let the researches in the new ranges of
temperature to be possible. The almost linear behavior of the resistance of platinum at the by then lowest
reachable temperatures (that of sublimation of hydrogen -it means 14 K-) recommended its use as a promising secondary thermometer which could be based on
calibrated conductivity measurements instead that of
helium, which presented its unpractical sizes as additional inconvenience. The first results were reported to
the Meeting of the Royal Netherlands Academy of Arts
and Sciences (KNAW) four months later. The main
objective of this first series of experiments, carried out
jointly with his assistant Jacob Clay (1882-1955) was to
prove the possible existence of a point of inflexion in the
curve representing the resistance as a function of temperature [60]. Platinum was chosen, at first instance,
as the standard metal [61]. This first communication
was followed by at least four related articles. Two of
them showed similar results with gold instead platinum
because the possibility to get it in a purer condition
[62] and the effect of admixtures on the electrical resistance [63]; the others included the study on the behavior, also as function of temperature, of expansion, a
property that was then believed to be related with resistances [64, 65]. From the beginnings the resistances
values were tabulated or plotted as ratios of the resistance at the observed temperature to the resistance at
a reference value (0 ◦ C or 273.09 K) versus absolute
temperature.
With the successful liquefaction of helium, the determination of electrical resistance of metals as a function of temperature became a priority for Kamerlingh
Onnes. The next objective at Leiden was the corroboration and extension of the new Dewar’s researches [66,
67], and others by Travers and his compatriot Alfred
G. C. Gwyer [68], on the subject at lower temperatures.
These results not only showed a continuous diminution
of the resistance of unalloyed metals as temperature
went down, but also would seem to suggest one of two
possible trends too; the reaching of a definite asymptotic value, unchangeable with additional decreasing of
temperature, or, following a dangerous extrapolation of
the available data, the absolute vanishing of resistance
at some temperature above absolute zero, or even a
negative resistance at this just value.
7.
Different theories about behavior of
the resistance of metals
Kamerlingh Onnes had doubts about what he could
expect from the following experiments. Although the
formulation of an appropriate theory for explaining the
2601-10
causes by which the phenomenon of contact electricity
is produced was one of the objectives of many physicists
in the last quarter of XIX century, all those by then existed were still in rudimentary state and left the doors
opened to any of the different possible forms of the temperature variation of the resistance (Fig. 8). The theory of the electrical and thermal properties of metals,
separately proposed by Eduard Riecke (1845-1915) [69]
and Paul Drude (1863-1906) [70], later refined by Hendrik Antoon Lorentz (1853-1928) [71], and based on arguments of classical mechanics, was very probably the
most successful. The theory proposed that electrical
resistance was a consequence of the thermal agitation
between the metal and the conduction electrons, which
led to a decreasing of resistance with temperature and
to a perfect conductivity of metals at absolute zero.
The electric current was treated as a drift of an electron gas under the influence of an electric field. The
free movement of the electrons (with a speed depending
of temperature) in the spaces between the heavy fixed
atoms of the metal with which they exchanged energy
by collisions, was restricted in some way in presence
of an imposed electric field, being the direction of this
latter which define the set up of the electric current.
Reif-Acherman
(1824-1907) as an inference from the theory of Riecke
and Drude [73]. The basic idea here was related with
the assumption of a decreasing density of the free electron gas as the temperature approached absolute zero,
being zero at this just value with electrons condensing (freezing) onto the atoms. The theory was widely
known at Leiden even before its publication at a British
journal, as it is revealed with its inclusion in a Jubilee
book coordinated by Kamerlingh Onnes on the occasion
of the retirement of his early professor Johannes Bosscha (1831-1911) (see Fig. 9) [74]. In practical terms,
the model suggested that the resistance of a conductor would reach a minimum somewhere in the curve
that represented its behavior, after which it would begin to increase until become ‘infinite’ at absolute zero.
Kamerlingh Onnes explicitly referred by first time to
the Kelvin’s proposal in his Address as Rector Magnificus in 1904 [13], and it seems that this model was in
some way the driver of the related researches in Leiden
until 1908.
Figura 8 - Possible (qualitative) forms of temperature variation
of electric resistance.
The constant and temperature independent minimized value of the resistance that characterized the
curve I was quickly associated by Kamerlingh Onnes
with impurity contents of the specimens under study.
He was able to confirm this behavior with platinum
as well with several species of gold of different grades
of purity. The fact, already known by Matthiessen
since 1864 [72], suggested the existence of a constant
residual resistance at helium temperatures, with values
which were lower the purer the specimens were. The
model corresponding to the curve type II emerged in
a proposal by William Thompson (later Lord Kelvin)
Figura 9 - Thanks letter addressed by Lord Kelvin to Kamerlingh
Onnes on occasion of the including of his paper in the Bosscha
Jubilee volume (1901). Credit: Courtesy of the Museum Boerhaave.
A recently published article, based on the study of
the surviving Kamerlingh Onnes’s original notebooks
housed at the Boerhaave Museum at Leiden, presents
a historical account of the technical details involved in
the experiments carried out between 1910 and 1911 [75].
The first successful resistance measurements at helium
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
temperatures were carried out in December 2, 1910, and
reported in February 1911 [76]. Previous experiences
had allowed the reaching of a new lower limit for temperature: 1.1 K. The physicists in charge of the experiments were Gilles Holst (1886-1968) and Cornelis Dorsman (1877-1960). Holst (Fig. 10), with some mechanical skills, graduated in mathematics and physics from
the Eidgenössische Technische Hochschule in Zurich in
1908 and previously assistant to the German physicist
Heinrich Friedrich Weber (1843-1912) in his researches
on specific heats, was the main responsible of the electrical measurements by operating a Wheatstone bridge
with the galvanometer; Dorsman assisted him with the
temperature measurements [77, 78].
Figura 10 - Gilles Holst (paint). Credit: Kamerlingh Onnes Laboratory; courtesy of the American Institute of Physics, Emilio
Segrè Visual Archives.
The metals under study were again platinum and
gold. The new experimental results quickly showed
Kamerlingh Onnes the inadequacy of Kelvin’s proposal,
and that, instead the resistance passing through a minimum, it approached to zero at a temperature near to
the absolute zero as it is schematically indicated by
curve III in Fig. 8. Kamerlingh Onnes proposed then
the thermal agitation of the oscillators introduced by
the German physicist Max Karl Ernst Ludwig Planck
(1858-1947) in his quantum theory of radiation as the
responsible mechanism for the new results [79]. In contrast to the Kelvin’s proposal, the electrons kept moved
around at those lowest temperatures, because it were
the oscillators that freeze and not the electrons. By
accepting the Planck’s vibrators as explaining element,
Kamerlingh Onnes followed the same line of thought
used by other researchers also working on behavior of
2601-11
other physical and chemical properties, such as Walther
Nernst (1864-1941) and his collaborators Arnold Eucken (1884-1950) and Frederick Alexander Lindemann
(1886-1957) in Berlin, with their investigations on specific heat of gases at liquid hydrogen temperatures [80],
and Albert Einstein with the recently developed theory
of specific heat of solid substances [81]. The researches
were to such an extent closely related each other that
some author dare to say that, by 1911, “Nernst and his
collaborators had thus advanced on the path toward an
early ‘discovery’ of superconductivity” [82].
8.
The decisive experiments
For the new experiments Kamerlingh Onnes proceeded
to implement some changes in his program in order to
solve technical inconveniences. On one hand, the older
arrangement of helium liquefier and cryostat, very similar to that used in 1908, was significantly modified.
In the new assembly, the liquid helium was transferred
from the liquefier to a separate helium cryostat, which
not only allowed the immersion there of the required
measuring instruments, but also the appropriate agitation of the contents and the corresponding keeping of resistances at uniform well-defined temperatures and the
handling of larger samples with incensing of sensitivity,
accuracy and easiness [83, 78]. Liquid helium handling
and transfer became a so ordinary procedure at the
physical laboratory at Leiden that it even coming to be
nicely caricaturized by members of the staff (Fig. 11).
On the other hand, it was decided to use mercury as
the metal to be studied instead the previous platinum
and gold. The reason was clear: the height of the leveling off of resistivity of metals at lower temperatures
that followed the section of its almost linear behavior
was clearly concluded dependent of the amount of impurities of the sample of metal used in the experiments.
Mercury clearly took shape as the best option because
of its facilities for to be repeatedly distilled in vacuum
at temperatures between 60 ◦ C and 70 ◦ C to an even
higher degree of purity than the other used metals, even
gold. There was no matter that mercury was liquid at
ambient temperature because it would freeze forming
something as a wire once the purified liquid was placed
in the glass capillaries, behaving then in the same solid
condition as the previously used metals.
Figura 11 - Helium procession with Kesselring followed by Kamerlingh Onnes; second from the right is Flim carrying the liquid
helium. Credit: Courtesy of the Museum Boerhaave.
2601-12
Using a empirically formula he had previously deduced on the basis of the Planck’s vibrators, Kamerlingh Onnes was able to theoretically predict that the
resistance of mercury should be lower at helium temperatures than at hydrogen temperatures and still dependent of temperature. These predictions joined to
what could be considered the main expectation, which
was the resistance should become, within the limits of
the experimental accuracy, zero at those low temperatures [76]. After some preliminary trials that included
very few experiments [84], the definitive experiences
were carried out on April 8, 1911. The equipment had
been again improved; the helium liquefier, which had
been expanded to enclose a platinum resistor, could
be now separated from the also new cryostat by closing a valve, and a double-walled vacuum pumped glass
siphon cooled by a flow of liquid air replaced the old
tube for liquid helium transfer. Figures 12 and 13 show
a schematic representation of the whole cryostat and
details of the mercury resistances, respectively. Figure
13a shows a portion of the leads of the mercury resistance partially filled with purified liquid mercury. It
was constituted by seven U-shaped tubes of about 0.005
mm2 cross section connected in series, joined together
by inverted Y-pieces sealed off above, and with platinum wires on both ends. Two leading tubes filled with
mercury, Hg 10 and Hg 40 , through which the current entered and left, were attached to the connectors in the
extremes (b0 and b8 -the last one not represented in the
original figure). At solidifying, this mercury formed
four leads of solid material. These leading tubes, as
well as those represented Hg 20 , Hg 30 could be used for
measuring the potential difference between the ends of
the thread. The lead Hg 50 was left as alternative for
measure the potential at b4 in order to evaluate possible variations of resistance along the full length of the
thread. Figure 13b shows the manner how the tubes
were really assembled inside the cryostat with the purpose of saving space for the stirring pump Sb . Figures
13c and 13d show the upper (in perspective) and front
views of the resistance as it was placed inside the cryostat, respectively. Figure 13e shows other type of leads
of mercury resistance, but with W-shape, used for the
extension of the experiments in 1912 for measuring the
resistance in four separate segments instead two.
The report of the series of measurements carried out
confirmed the predictions, as it can be read (the original notation is preserved): “The value of the mercury
resistance used was 172.7 Ω in the liquid condition at
0 ◦ C; extrapolation from the melting point to 0 ◦ C by
means of the temperature coefficient of solid mercury
gives a resistance corresponding to this of 39.7 Ω in the
solid state. At 4.3 K this had sunk to 0.084 Ω that is,
to 0.0021 times the resistance which the solid mercury
would have at 0 ◦ C. At 3 K the resistance was found
to have fallen below 3 x 10−6 Ω that is to one tenmillionth of the value which it would have at 0 ◦ C.”
Reif-Acherman
[85].
Figura 12 - Schematic view of the cryostat used for experiments
with mercury in 1911 [83].
Because the abrupt fall in the resistance, not predicted by his theoretical formula, between the melting
point of hydrogen and the boiling point of helium observed in the measurements with mercury, especially
between 4.21 K and 4.19 K, Kamerlingh Onnes got
quickly involved in a new series of experiments in a narrower range of temperatures, in order to obtain more
accurate potential measurements, and “establish beyond all possibility of doubt” that the resistance became practically zero. The main hypothesis was focused on the probable existence of an inflection point
in this range of the curve representing the resistance as
a function of temperature. The new experiences, which
began six weeks later on May 23, and extended to October, not only confirmed the previous conclusions but
also allowed an explicit reference to the jump in resis-
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
tivity. The results communicated at the Meeting of the
Academy on November 25 and published the following
month indicated that while the decreasing of the resistance was gradual between 4.29 K and 4.21 K, it was
significantly rapid between 4.21 K and 4.19 K, disappearing at this latter value.
Figura 13 - Details of the mercury resistance and leads [87, 88].
Figura 14 - Historical graph showing the jump in absolute resistance (Ω) of mercury in the vicinity of 4.2 K [87].
2601-13
According to an entry in the Kamerlingh Onnes’s
notebook, the experiences included the study in reverse
direction; it means from lower to higher temperatures:
“At 4.0 [K] not yet anything to notice of rising resistance. At 4.05 [K] not yet either. At 4.12 [K] resistance
begins to appear” [75]. The details associated with
this procedure recently became the subject of a sort of
polemic created about the possibility that the discovery could to have been similarly to helium liquefaction
the consequence of an accidental inattention and not of
a programmed step in the experimental program. An
anecdote of second hand told by an older visitor of the
laboratory at Leiden indicate that the student of the
School for Instrument Makers in charge of the differential oil manometer used to control the vapor pressure
inside the cryostat was nodding off and the pressure
started so to increase from below the boiling point of
helium to about 4.2 K. As the transition temperature
of mercury was in the route, it was obvious that a sudden movement of the light beam of the galvanometer
must to have happened, showing then the restoration
of the electrical resistance of the metal [86]. In the author’s opinion there is not enough primary information
to support or not this historical possibility.
The report of December 1911 included the historically known graph of resistance (now in absolute ohms)
as a function of temperature [87]. It seems that the
use of absolute resistance instead the, until then, usual
ratios, was due to the uncertainty in the extrapolation
to the resistance of solid mercury at 0 ◦ C from its value
at the melting point. Kamerlingh Onnes named initially the new phenomenon “supraconduction” to difference the conduction process of the variable conductivity which represented the conductance of a determined
material.
It was clear that some “special phenomena” related
with the unexpected behavior of mercury at those extreme temperatures were still obscure and that the
studies should continue, as it effectively happened.
Kamerlingh Onnes published several papers in the following years related with the new phenomenon. They
were related with different concepts, such as critical
current density and the associated potential difference,
which, with the course of time, would become one of the
most important for practical applications, the influence
on them of different variables, as well the superconducting nature of other metals such as tin and lead [88-90].
Some of the several successive events that followed the
discovery arouse curiosity and confusion. He was, for
example, surprised to find that after so much care he
put for purifying mercury, the simple adding of gold
and cadmium to the same element did not stop it from
entering the superconducting state. On the other hand,
he was strongly disappointed within a couple years of
his discovery; he found that a supercurrent could to be
destroyed by even a small magnetic field. Some of his
developments, such as the persistence over a long pe-
2601-14
riod of time of a current created in a close circuit made
with the new superconducting materials even after the
corresponding battery had been removed, suggest him
only very few of the almost unlimited number of technological applications [91] that would begin to became
reality more than three quarters of a century later [92].
9.
Concluding remarks
Liquefaction of helium opened a new subject of study of
low temperature physics. At referring to great transformations of his original idea at undertake his research at
low temperatures in an address delivered in 1922 before
the Faraday Society and the British Cold Storage and
Ice Association, Kamerlingh Onnes stated that “the extension and importance which the work in this direction
has attained, has widely surpassed any anticipation of
mine” [93]. Indeed it was so. Many questions about
the constitution of matter and the universe have been
answered by the study of the phenomena at the temperatures made possible by liquid helium.
As it can be said that liquefaction was the triumph
of a systematic and very careful planned work, superconductivity was the unexpected finding of a program
of research with almost all predictable results. The discovery of superconductivity, as well superfluidity and
other events that came later, were the beginning of
a torrent of technical developments that very quickly
covered multiple areas. Several centers of investigation
throughout the world quickly included superconductivity as a central subject of research [94]. A contemporary review on the state of the art of the subject, six
decades after the discovery, reflects well the real development [95]. Semiconductor devices, superconducting magnets, magnetic resonance imaging, rocket fuels,
cooling of nuclear particles, storage of biological materials, infrared sensors for target location and guidance in
anti-satellite rockets, are only few of the great number
of application examples of liquid helium and of technical improvements that only few decades ago began to
change the style of life of the society [96]. The discovery of the high temperature superconductivity in 1986,
which stimulated what has been called the revolution of
these kinds of materials, decisively contributed to settle even more the striking character of the new subject
[97].
In those times the new phenomenon could not be,
nevertheless, theoretically understood, and its practical usefulness was considered null. Kamerlingh Onnes
himself made a weak attempt for supply a theoretical
explanation for superconductivity based on the supposition that the new established phenomena might be
of quantum nature, according to the Einstein heat capacity theory. Quantization, as he referred in the Nobel
Lecture, had introduced in physics a possibility for contribute in a fundamental way to the solution of problems related with several investigations into properties
Reif-Acherman
of substances at low temperature. Although his trial
for contributing theoretically to the solution was unsuccessful, very probably because the difficulty to divorce himself so late in his career from classical concepts, he was more fortunate in predicting that his discovery could contribute someday for that wires carry
electricity to consumers, providing so a cheap and almost unlimited supply of electricity [98]. For decades no
one was able to explain how the effect worked, at such
extreme that some author refers to it as “the shame
and despair of theoretical physics” [99]. The German
physicist Fritz London, who with his brother Heinz was
the first to recognize superconductivity and superfluidity as resulting from manifestations of quantum phenomena on the scale of large objects, was clear about
how classic physics represented a prejudicial attitude
that hindered the development of an appropriate theory. At propose the phenomenological first theory of
the electrodynamics of a superconductor, he concluded:
“The present historical situation may be characterized
in such a way that it is rigorously demonstrated that,
on the basis of the recognized conceptions of the electron metals, a theory of superconductivity is impossible
- provided that the phenomenon is interpreted in the
usual way (i.e. as a kind of limiting case of ordinary
conductivity) [100]. It was only in 1957, more than
four and half decades later and after several constructive developments [101], when the American physicists
John Bardeen (1908-1991), Leon Neil Cooper (1930-)
and John Robert Schrieffer (1931-) provided an appropriate microscopic description (BCS theory) of the new
phenomena [102].
Although the exact justifying words by which the
Nobel Committee granted Kamerlingh Onnes the Nobel Prize in Physics in Stockholm on December 19, 1913
(“for his investigations on the properties of matter at
low temperatures which led, inter alia, to the production of liquid helium”) don’t made explicit reference to
superconductivity, he will be ever remembered in the
annals of the history of physics as the responsible of
what is considered one of the more dramatic instances
in the history of low-temperature physics and to which
Martin and B. Ruhemann refer in their book Low Temperature Physics as “the kind of phenomenon that every
physicist would like to have discovered” [103].
Acknowledgments
I thank the Museum Boerhaave for providing permission to reproduce several figures in the text and Mr.
Harja Blok, Editor in chief of Refrigeration and Climate Control / Koude & Luchtbehandeling, for supply the photograph of the commemorative stone for
the liquefaction of helium in my paper. I also thank
the Friends of the Center for History of Physics and
the Emilio Segrè Visual Archives of the American Institute of Physics, the Kamerlingh Onnes Laboratory
Liquefaction of gases and discovery of superconductivity: two very closely scientific achievements in low temperature physics
and the Nobel Foundation for their kind permission
to use the painting of Gilles Holst, the photograph of
Heike Kamerlingh Onnes, and the diagram of the cascade process, respectively.
2601-15
[11] J. Dewar, Proceedings of the Chemical Society 13, 186
(1897), reprinted in G.D. Liveing, and J. Dewar, Collected Papers on Spectroscopy (Cambridge University
Press, London, 1915), p. 473-476.
[12] S. Reif-Acherman, Physics in Perspective 6, 197 (2004).
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